Conventionally, there has been proposed one recording device for forming images on a recording medium such as paper. The device employs a recording material in the form of powder, made of toner and carrier. Typically, a particle size of the carrier is greater than that of toner. The device includes a bearing member for bearing the recording material, a backing electrode spaced a distance from the recording material born on the bearing member, and a substrate lying between the bearing member and the backing electrode. The substrate is formed with apertures through which the toner can pass and is provided with a plurality of individual electrode, each of which individual electrodes surrounding the aperture.
In such recording device, the toner and carrier are charged with opposite polarities by the contact with each other. In operation, a voltage having a polarity different from that of the toner is applied to the backing electrode, which forms an electric field for forcing the toner toward the backing electrode. An intensity of the electric field is not sufficient for the toner to separate from the carrier retaining the toner electrically.
In this state, once a voltage having a polarity different from that of the toner is biased to the selected individual electrode, the electric field is enhanced in the vicinity of the biased individual electrode. This enhancement of the electric field allows a part of toner opposing to the biased individual electrode to separate from the carrier and then propel toward the backing electrode through the corresponding aperture. Then, the toner passed through the aperture adheres onto a recording medium such as paper running between the plate and the backing electrode.
With this arrangement, the carrier made of magnetic material is normally held on the bearing member by a magnetic force generated between the carrier and the bearing member, though; a small amount of it can separate from the bearing member to drop onto the plate due to mechanical and electrical vibration, for example. Particularly, where the bearing member is supported above the backing electrode, more carrier will drop from the bearing member onto the substrate with the aid of the gravity applied thereto. Disadvantageously, the carrier on the plate may block the apertures due to its particle size that is greater than aperture. Eventually, this prevents the toner particles from the toner particles from being propelled through the blocked apertures, resulting in dot- defects degrading the resultant images.